Attiny85 Digispark USB is the smallest Arduino compatible development board so far. Originally developed under the name Digispark and released under open source license. It has 6 port with several functions. Depending on the programming (with Arduino IDE) can it have 6 digital I/O, 4 analog inputs or 3 PWM outputs. It can be powered by a USB port or an external power supply of 6…35V DC.
Attiny85 Digispark USB specs:
Support for the Arduino IDE 1.0+ (OSX/Win/Linux) Power via USB or External Source – 5v or 7-35v On-board 500ma, 5V Regulator Built-in USB 6 I/O Pins 8k Flash Memory (about 6k after bootloader) I2C and SPI (vis USI) PWM on 3 pins (more possible with Software PWM) ADC on 4 pins Power LED and Test/Status LED
For more information, please follow the link to the official Digispark product page: klick here.